oe4 
NATURE 
[AUGUST 29, 1912 
liber Aiea in the process of condensation, which 
will tend to set up convection currents. 
Prof. J. von Hann’s opinion on the subject, 
in the latest edition of his “Handbuch der 
Klimatologie” is that the question cannot be 
definitely answered at present, but that the effect, 
if any, should be greater in the tropics than in 
higher latitudes. Dr. G. T. Walker, of the 
Meteorological Office, Simla, is of a similar 
opinion. He states that if forests have any in- 
fluence at all on the rainfall, it is probably not 
ee | in India than 5 per cent. Rac: 
AND THE ELECTRIC THEORY 
OF MiETG ETT 
N Sir John W. F. Herschel’s classical article 
on light (dated 1827) in the “ Encyclopedia 
Metropolitana ” of 1830, p. 439, there is a vague 
reference to a theory of light then recently pro- 
pounded by Oersted, in which he sought to explain 
the nature of light-waves as a succession of minute 
electric sparks. Desiring to follow up this refer- 
ence, the writer of this notice consulted, but fruit- 
lessly, all the writings of Oersted within his reach. 
Thereupon he applied for information to Prof. 
Absalon Larsen, of Copenhagen, who, after con- 
sultation with Prof. Christiansen, kindly directed 
the writer to sources not available in London, and 
furnished the extracts now given from Oersted’s 
writings, 
The theory of light suggested by Oersted was 
first advanced in a remarkable book, written in 
the German language, and published in Berlin 
in 1812, under the title, “ Ansicht der chemischen 
Naturgesetze,’ von H. C. Oersted. The theory 
of light occupies only a small part of this book 
(298 pages in all), which is of a much wider scope. 
Oersted proposes to refer all chemical phenomena 
to fundamental agents (forces), hoping thus to 
initiate a development of theoretical chemistry 
analogous to the development which the intro- 
duction of simple laws had brought about in 
mechanics. A quotation from his own introduc- 
tion, pages 7-9, will state the position :— 
It will not be without use here at the outset to 
review the whole road to be travelled. We intend to 
make the beginning of our investigation with a 
demonstration and arrangement of all bodies accord- 
ing to their chemical nature. Then we will set forth 
some considerations about the ordinary chemical 
actions known to us, and will show from them that 
all chemical changes 
referred to two widely extended forces of Nature. 
We will at the same time demonstrate that these 
forces are able to act not only by direct, but also by 
indirect, contact; that consequently they can be con- 
ducted. This will lead us to those chemical circuit- 
actions which have already been known to us for a 
long time in Galvanism. And, lastly, this will bring 
us on to demonstrate chemical forces in their free 
activity, and so at the same time to make evident 
their identity with electrical forces. Here, then, we 
shall reverse the course of our investigation, and 
directing our attention to electrical forces, 
seek to discover how these also can be related to the 
chemical form of action. And besides we then be- 
come aware that the electric forces, like the chemical 
NO. 2235, VOL. 89| 
OERSTED 
hitherto investigated can be | 
we shall | 
| heat and 
ones, are two, and that they at the same time are 
opposed; that both are of general application, and 
that, from the state of relative rest in which they 
exist in bodies, they can pass over into activity when 
aroused by external forces... . / After we have in 
this way set forth the broad connection of chemical 
and electrical actions, in these two opposite direc- 
tions, we shall, relying on an investigation into the 
nature of conduction, try to show under what con- 
ditions the two forces produce Heat, and under what’ 
conditions they produce Light. We shall thereby re- 
gard these great phenomena in a far more intimate 
connection with the rest of nature than were possible 
according to the ordinary view. 
Starting from the nature of electric conduction, 
Oersted then attempts to show the conditions 
under which the two opposing agencies produce 
light respectively. His ideas about 
conduction he develops on pages 138, 139 :— 
If, therefore, one of the electric forces is pro- 
pagated through space, this occurs in the following 
way: that it attracts the opposing force in the 
nearest zone, binds it, and itself in turn suffers a 
diminution from it, in ¢onsequence of which the next 
zone receives actually the overplus of the same force 
as it spreads, but itself excites a new zone of the 
opposing force, so as again to react, and so forth. 
One may express all this by saying that Electricity 
is propagated by wave-motion (die Electricitét 
verbreitet sich undulatorisch). 
As to the conditions under which the conduction 
of electricity produces heat, Oersted writes on 
pp. 164-165 :— 
We have seen that Conduction consists in a dis- 
turbance running through all points of the body and 
in a restitution of equilibrium. So long as the Con- 
duction is complete, the restitution will always be 
brought about by the mutual attraction of the force 
evoked out of equilibrium. But when by reason of 
a forced conduction a greater quantity of force pene- 
trates the body than the latter is able spontaneously 
to conduct away, then at once the interiorly-disturbed 
equilibrium cannot be restored again by the body’s 
own forces. ... This condition, in which equi- 
librium is disturbed at every point of the body, but 
in such wise that no recognisable separation of the 
forces is attained, gives us the phenomenon of 
Jeli 6-08 
To distinguish it from other theories of heat, 
the mechanical, which regards heat as a vibration 
of material particles, and the chemical, which 
assumes a particular substance (caloric), Oersted 
calls his own the dynamical theory. 
As regards light, Oersted first shows that heat 
may be transformed into light, and vice versa, 
and he therefore considers heat and light as pro- 
duced by the same two agencies. The difference 
is that, as stated above, for the production of 
heat no real separation of the two agencies is 
needed, whereas for the production of light the 
tension of the opposite forces or agencies must 
reach its maximum value and produce a discharge. 
The following passages are from p. 222 :— 
. sO We must content ourselves with knowing 
that Light will be produced if the tension of opposi- 
tion of ‘the internal forces has attained its maximum 
| and passes over into equalisation. 
| 
: 
